Free-living amoebae (FLA) are opportunistic protozoa widely distributed in the environment. They are frequently found in water and soil samples, but they have also been reported to be associated with ...bacterial human pathogens such as Legionella spp. Campylobacter spp or Vibrio cholerae among others. Including within Vibrio spp. V. harveyi (Johnson and Shunk, 1936) is a bioluminescent marine bacteria which has been found swimming freely in tropical marine waters, being part of the stomach and intestine microflora of marine animals, and as both a primary and opportunistic pathogen of marine animals. Our aim was to study the interactions between Vibrio harveyi and Acanthamoeba castellanii Neff. Firstly, in order to analyze changes in it cultivability, V. harveyi was coincubated with A. castellanii Neff axenic culture and with Acanthamoeba Conditioned Medium (ACM) at different temperatures in aerobic conditions. Interestingly, at 4 °C and 18-20 °C bacteria were still cultivable in marine agar, at 28 °C, in aerobic conditions, but there weren't significant differences comparing with the controls. We also noted an enhanced migration of Acanthamoeba toward V. harveyi on non-nutrient agar plates compared to controls with no bacteria.
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•Vibrio harveyi culturability was not significantly improved after incubation with Acanthamoeba castellanii Neff.•Acanthamoeba castellanii Neff seems to present a chemoattraction to Vibrio harveyi inoculum.•Acanthamoeba could play a role as vehicle of Vibrio harveyi in the environment.
In the future power system based on active distribution grid, allowing some portion to be disconnected, the concept of universal wind turbine systems may arise. This concept covers both ...grid-connected and island operations. This may happen if the voltage goes outside the range recommended by the standards. In such conditions, an island is constituted where the universal wind turbine is capable to manage the local voltage and frequency assuring the continuous supply to local loads. In this paper, a control loop based on droop and voltage controllers disposed in cascade is employed in both operation modes. Droop control offers power load sharing between the distributed generation sources connected in parallel in the island. The voltage controller is designed to provide smooth transitions between modes and power quality. A synchronization system is also introduced for assuring safe reconnections with the main utility. Simulation and experimental results are presented to verify the performance of the complete system.
Wind Turbine (WT) systems based on Permanent Magnet Synchronous Generators (PMSG) have become important mainly due to their high power factor and high efficiency. In order to reduce costs, ...maintenance and complexity, speed and position estimators can be used to replace the corresponding sensors in low and high power WT. This paper studies a PMSG flux observer, which is used along with a PLL to estimate both rotor speed and position. The robustness of the sensorless technique is analyzed against the PMSG parameters variation at low speeds, which it is usually the most problematic condition.
Chemotherapy is effective against a wide variety of tumor cells, although its use is limited by side effects. In vitro experiments and phase I and II trials have shown that phytochemicals such as ...perillyl alcohol (P-OH) have antitumor effects. Pentoxifylline (PTX), a synthetic methylxanthine used mainly to treat pathologies associated with hematological diseases, sensitizes tumor cells to chemotherapy. The aim of this study was to determine whether PTX amplifies the antitumor effects of P-OH in U937 human myelomonocytic leukemia cells.
Apoptosis was measured by the loss of mitochondrial membrane potential determined by flow cytometry using dihexyloxacarbocyanine iodide (DiOC6) and propidium iodide. Bcl-2 and Bax protein expression was also assessed by Western blot analysis.
P-OH and PTX induced loss of the mitochondrial membrane potential in U937 cells in vitro. Culturing the cells in the presence of both compounds caused a significant increase (p < 0.001) in apoptosis and expression of anti-apoptotic Bcl-2 and pro-apoptotic Bax proteins. However, despite their coexistence, Bax expression prevailed in our experiments. These data suggest that the effects of PTX might be attributable to changes in the mitochondrial membrane potential.
PTX sensitizes tumor cells to the anti-neoplastic action of P-OH. These observations may have clinical relevance in the treatment of cancer patients.
The control of grid voltage and current source converters (VSCs and CSCs) in stationary reference frames by means of resonant controllers is a well-known issue. The corresponding sinusoidal control ...references should be also limited under anomalous conditions to assure the safe operation of the converter. Present saturators, designed for synchronous reference frames, limit the reference but not its amplitude or phase which distorts sinusoidal waveforms and changes the a priori active and reactive power references. This work is focused on developing different novel techniques achieving different grades of distortion and bandwidth in function of the control loop structure and system requirements. Tools like Kalman Filter (KF), second order generalized integrator (SOGI) and phase-locked loop (PLL) or vector calculus are employed to develop these saturators. Simulation and experimental results are provided to verify the saturators performance in several control systems.
Signal processing algorithms like IIR filters applied to distributed power generation system must be programmed in fixed-point in the most of cases. This arithmetic causes errors due to the ...quantification. In z-domain implementations, for high sampling frequencies, poles very close to the unit circle can move to the unit circle bringing about an unstable behavior. Nevertheless, IIR filters implementations based on delta operator reach higher performance when the sampling time is small due to the stability region become similar to continuous time-domain. This operator permits to reduce quantification effects of the coefficients, to use smaller word length, to increase the efficiency and to reduce the resources consumed. In this paper, a study of IIR filter quantification and delta operator is carried out. As example, fixed-point implementation of second order generalized integrators (SOGIs) is realized, whose results show the advantages of using delta operator.
In this paper, two current controller schemes, based on repetitive controllers and proportional+resonant controllers using second order generalized integrators connected in parallel, are proposed and ...compared for shunt active power filters. Both controllers are well suited due to their optimum tracking and harmonic rejection capability. The objectives of this paper are: to analyze both controllers in the continuous and discrete time-domains; to study how to tune the parameters of the controllers and other auxiliary elements like PI controller in the case of repetitive-based controller; to show questions related to real-time implementation for the two cases; and, finally, to present some experimental and comparative results.
This paper realizes an exhaustive analysis and comparative study about the different existing techniques up to now in order to develop repetitive-based controllers applied to selective harmonic ...compensation in shunt active power filters. Starting from the generic repetitive controller, the advantages and drawbacks of the different versions that have arisen from the original model are compared. The paper also explains the importance of having a correct and accurate model of the plant in order to ensure stability and good performance of the entire system, justifying the method used to carry out the design of such model. The response of different controllers is compared in presence of disturbances, variations in the nominal value of the plant parameters and the computational load.
This paper introduces a novel approach to estimate the initial rotor position in permanent magnet synchronous generator (PMSG) sensorless drives. The main problems of sensorless techniques appear at ...low speeds and also at standstill. To ensure a stable starting, this paper presents firstly an overview of several techniques for initial rotor position estimation (IRPE) proposed previously by other authors, and secondly a new algorithm based on the position dependence of the current response. Besides, a method to obtain the magnetic orientation is also included. A comparison between all techniques analyzed in this paper is carried out and lastly, the experimental setup where the results will be obtained is presented showing a proposal to implement the new algorithm.
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